If your anchor point is too weak then there's really not much you can do about it. Any contraption a single person can easily set up in their home with hand tools will just as easily collapse due to gravity while trying to support an entire human being suspended in mid-air. As a rule of thumb, if you can shake it with your hand and wiggle it around then it's probably too weak to support your weight. You'd need something really sturdy, such as an attic beam, for full peace-of-mind.
Finding a sturdier anchor point in a publicly-accessible location is the only solution if there are no suitable anchor points inside. It's an unfortunate truth but a truth nonetheless. Naturally, you'd want to do it at night (ideally a new moon to minimise light levels) at a place which sees little human activity during the night (forests, construction sites, and industrial estates are all good) and CTB there. If it's within walking/cycling distance then that would be ideal as using a car can attract attention and public transit might not even be available at night.
A dog leash is also not an appropriate ligature. The ideal ligature is a braided polyester rope which is thick enough to not dig into your skin but also not so thick that you cannot tie it into a noose. Please refer to
this thread (where the information for my own full-suspension CTB plan comes from) for more information.
Best Wishes,
CumbriaCTB
